Half-Lives of AST & ALT Relative to Hepatocellular Injury

 

If the decline in serum concentrations follows first order kinetics:

 

concentration at time T =

= (initial concentration in mg/dL) * EXP((-1) * k * (T in hours))

Transaminase	Half-Life in Hours	k value
AST	16 hours	0.043
ALT	48 hours	0.0144

 

The time required to decline to normal (serum concentration <= upper limit of normal reference range) is:

 

expected time to normalize in hours =

= LN((initial serum level) / (upper limit of normal reference range)) / k

 

Interpretation:

• If the serum level has normalized within the expected time, then hepatic injury was transient.

• If the serum level has not normalized, then hepatic injury may be ongoing.